<p>Phase change materials have excellent heat storage capacity, which is a great advantage in utilizing clean energy and improving the efficiency of energy use. However, the leakage issue of solid–liquid phase change materials limits their application. In this study, Arundo donax cv. Lvzhou No.1 (LZ1) was utilized to fabricate a porous biomass carbon skeleton, into which polyethylene glycol (PEG) was introduced via vacuum impregnation to address the PEG leakage issue during phase change and enhance thermal conductivity. The prepared shape-stabilized composite phase change material (ss-CPCM) was characterized and tested for its adsorption rate and thermal conductivity. The results of BET, SEM and leakage experiments showed that PEG can be well adsorbed in the pores of carbonized LZ1 (CLZ1). FT-IR and XRD analyses confirmed the physical interaction between PEG and CLZ1. The results of DSC and thermal conductivity tests yielded that the composite phase change material has a high latent heat value (134.74&#xa0;J&#xa0;g⁻¹), and its thermal conductivity was improved by about 78.12% compared with that of PEG. Thermogravimetric and thermal cycling experiments demonstrated that the prepared composite phase change materials have good thermal stability and still have good energy storage capacity after many thermal cycles. The prepared PEG/CLZ1 ss-CPCM is an economical, energy-saving and sustainable phase change material with potential applications in the field of building energy efficiency.</p>